regcomp brings in references to wcscoll, which isn't in all the standards that contain regcomp. In turn, wcscoll brings in references to wcscmp, also not in all those standards.
[initial] regcomp -> [libc.a(regex.o)] wcscoll
[initial] regcomp -> [libc.a(regex.o)] wcscoll -> [libc.a(wcscoll.o)] __wcscoll_l -> [libc.a(wcscoll_l.o)] wcscmp